1. Field of the Invention
The present invention relates generally to a capacitor, and more particularly, to a capacitor with multiple anodes connected to a common terminal inside the capacitor casing. This makes the present capacitor more readily adaptable to automated manufacturing techniques. The goal is to build highly reliable capacitors at a reduced unit cost through an improved connection of multiple anodes before they are associated with a cathode.
2. Description of Related Art
As more and more medical applications are investigated and implemented to aid and assist the human body, devices needed to deliver the desired therapy are becoming increasingly more sophisticated, both functionally and in terms of their structural makeup. Modern implantable devices require power sources that are smaller in size, but powerful enough to meet the therapy requirements. For example, a cardiac defibrillator has a battery powering circuits performing such functions as, for example, the heart sensing and pacing functions. This requires electrical current of about 1 microampere to about 100 milliamperes. From time-to-time, the cardiac defibrillator may require a generally high rate, pulse discharge load component that occurs, for example, during charging of a capacitor assembly in the defibrillator for the purpose of delivering an electrical shock to the heart to treat a tachyarrhythmia, the irregular, rapid heartbeats that can be fatal if left uncorrected. This requires electrical current of about 1 ampere to about 4 amperes.
The current trend in medicine is to make cardiac defibrillators, and like implantable devices, as small and lightweight as possible without compromising their power. This, in turn, means that capacitors contained in these devices must be readily adaptable in how they are connected to each other as well as to the battery and the device circuitry. In that light, a number of patents and publications disclose electrical energy storage devices including capacitors having a dual anode structure.
One is U.S. Pat. No. 6,850,405 to Mileham et al., which is assigned to the assignee of the present invention and incorporated herein by reference. This patent relates to a design that provides two anodes with associated feedthrough wires having their own glass-to-metal seals. As long as they are electrically insulated from each other, the feedthrough wires can also be combined into one glass-to-metal seal. One embodiment has the two anode feedthrough wires left unconnected outside the capacitor. In another, they are joined externally of the capacitor casing. Several interconnect designs are described, none of which include a connection of the anode leads within the capacitor casing.
U.S. Pat. No. 7,012,799 to Muffoletto et al., which is also assigned to the assignee of the present invention and incorporated herein by reference, describes an enclosure for a wet tantalum electrolytic capacitor or for an electrochemical cell such as a lithium/silver vanadium oxide cell. In one embodiment, the capacitor comprises a metallic enclosure of a first drawn portion, and a second stamped cover. The enclosure houses two anodes in a side-by-side relationship. Each anode includes an embedded anode wire weld contacted to an anode lead electrically insulated from the casing by a glass-to-metal seal. The anode wires are not connected within the capacitor casing.
U.S. Pat. No. 6,679,926 to Kajiura et al., which is incorporated herein by reference, describes a lithium secondary battery including a cathode of a porous sintered material made of a lithium-transition metal oxide in electrochemical association with several pairs of anodes made of a sintered material joined onto a rectangular anode current collector. The anode current collector has a strip-shaped anode lead that protrudes at one end thereof. In an electrode assembly, a plurality of extending anode leads is bundled into an anode-connecting conductor welded onto an anode terminal via an insulation plate.
U.S. patent application Ser. No. 11/615,410 Ziarniak et al., which is assigned to the assignee of the present invention and incorporated herein by reference, discloses a capacitor comprising a casing of first and second casing members, a feedthrough wire electrically insulated from the casing and extending there from, first and second anodes electrically connected to each other within the casing by an anode wire extending between them, a cathode, and an electrolyte. A second anode wire connects either to the first anode wire and serves as the feedthrough wire passing through a glass-to-metal seal or it connects to one of the anodes themselves before subsequently connecting to the feedthrough wire.
However, the Ziarniak et al. patent application requires that the anode wires are embedded within the anode pellets during the pressing process. This makes the pressing process relatively difficult to automate. In an alternative embodiment, the anode wires are welded to the peripheral edges of the anode pellets. This secondary operation is also difficult to automate, and increases manufacturing cycle time. For both of these embodiments, after wire bonding of the anode pellets to each other, it is also difficult to accurately position the anodes when assembling them with a corresponding cathode foil and separator material.
What is needed, therefore, is a capacitor having multiple anode pellets that can be formed simultaneously using automated equipment, connected together with highly accurate positioning, and easily assembled with a corresponding cathode into an anode/cathode assembly.